Repetition of images

[sredford]

Sometimes the bot tweets the same image again. I have noticed/suspected it a couple of times, now here is hard evidence:
https://twitter.com/Sentinel2Bot/status/816264394502008840
https://twitter.com/Sentinel2Bot/status/814858131440336896
There are probably many more, because I must only notice it when it's a distinctive image and when it gets repeated quickly.
Is this understood?

• cycles through not enough images?
• falls back (when cloudy) to 'default' images?
• random number generator not random?

Could it be tested? eg, download all the word parts of the tweets and compare?